1. Field of the Invention
The present invention generally relates to an apparatus and method for heat-treatment of an optical fiber reinforcing member, which reinforces optical fibers by covering a fusion-splicing portion therebetween with a sleeve-like protection member and by heat-shrinking the sleeve-like protection member, and to an optical fiber fusion-splicing apparatus.
2. Description of Related Art
Hitherto, the fusion-splicing of optical fibers has been performed by removing a fiber coating from a connecting end of each of the fibers and by heat-fusing exposed butting end parts of the bare fiber portions. The fusion-spliced bare fiber portions, from each of which the fiber coating is removed, are weak in mechanical strength and thus protected by reinforcing members. These reinforcing members are usually constituted by accommodating a thermal melting tube made of a thermal melting resin, to which a tensile strength member (referred to also as a reinforcing rod) is attached, in a heat shrinkable tube adapted to shrink in a radial direction by being heated (see , for example, JP-A-9-297243 (FIGS. 4 and 6 and the description thereof)).
FIGS. 15A to 15C are views illustrating the conventional method for heat-treatment of a fusion-splicing portion, which is disclosed in the JP-A-297243. More particularly, FIG. 15A is an explanatory view illustrating an example of a general reinforcing member. FIG. 15B is a view illustrating an example of heat-treatment using a V-grooved heater support. Further, FIG. 15C is a view illustrating an example of heat-treatment using a U-grooved heater support.
In an example of single optical fibers shown in FIG. 15A, the fiber coatings of the connecting ends of both optical fibers 1 to be fusion-spliced to each other are removed therefrom to thereby expose bare fiber portions thereof. Then, the leading ends thereof are butted against each other and then fusion-spliced to each other by arc-discharge or the like. The reinforcing member 6 has a length sufficient to cover a predetermined range of each of the fiber coatings left at both sides of the spliced bare fiber portion. The reinforcing member 6 is constituted in such a way as to accommodate a thermal melting tube 4 made of a thermal melting adhesive and also accommodating a crescentic tensile strength member 5 in a heat shrinkable tube 3. The fusion-spliced optical fiber 1 is inserted into the thermal melting tube 4 so that the fusion-spliced portion 2 is positioned at the center thereof. Then, the fusion-spliced optical fiber 1 is heat-treated on a flat heater support 9.
FIGS. 15B and 15C illustrate examples of reinforcement of a fusion-spliced portion of an optical fiber ribbon 1′. In these cases, a reinforcing member 6′ is constituted in such a way as to accommodate a thermal melting tube 4 made of a thermal melting adhesive and also accommodating a tensile strength member 5′ in a heat shrinkable tube 3, similarly to that shown in FIG. 15A. Further, optical fiber ribbons 1′ are disposed on both sides of the tensile strength member 5′ to thereby collectively reinforce plural fusion-splicing portions. A heater support 9′ shown in FIG. 15B is formed so that surfaces thereof, on which the reinforcing member 6′ is accommodated and placed, are constituted by those of a V-shaped cross-sectionally formed V-groove 7. Furthermore, a heater support 9′ shown in FIG. 15C is formed so that surfaces thereof, on which the reinforcing member 6′ is accommodated and placed, are constituted by those of a U-shaped cross-sectionally formed U-groove 8. Incidentally, the heater support 9′ having the V-groove 7 or the U-groove 8 can be used in the case of employing the single optical fiber 1 shown in FIG. 15A.
The reinforcing member 6′ is heated by heat transmitted from the concave wall surfaces that are constituted by the V-groove 7 or the U-groove 8. Thus, the heat shrinkable tube 3 heat-shrinks and reduces space-capacity therein. Simultaneously, the thermal melting tube 4 melts, so that the space in the heat shrinkable tube 3 is filled with the molten resin, and that the exposed fusion-spliced portion and peripheral parts thereof are surrounded by the molten resin. Thereafter, the molten thermal melting tube 4 becomes solidified. Thus, the heat shrinkable tube 3, the tensile strength member 5′, and the optical fiber ribbons 1′, which includes the fusion-spliced potion, are united, so that the reinforcement is completed. It is described that as compared with the case of heating the reinforcing member 6′ by using the heater support 9 having a flat heating surface as shown in FIG. 15A, a uniform and efficient heat-treatment can be performed by employing, when heating the reinforcing member 6′, the concave wall surfaces constituted by the V-groove 7 or the U-groove 8 as the heating surfaces of the heater support 9′.
However, the reinforcement of fusion-splicing of optical fibers is performed on those of a large variety of optical fibers from the single optical fiber to the optical fiber ribbon. Thus, the diameter of the reinforcing member varies with the optical fibers. For example, in comparison with a case where the diameter of a cross-section of a reinforcing member for the single optical fiber is about 4 mm before shrinkage thereof, that of a cross-section of a reinforcing member for 16-fiber to 24-fiber optical fiber ribbons is 8 mm. Therefore, generally, it is necessary to manufacture and prepare for heaters that are made of a material, such as metal and ceramics, and respectively provided with concave heating portions having various sizes. Thus, this reinforcement has problems with cost and management.
In contrast with this, there has been also known an example of bending a flexible sheet-like heating body like a letter “U” and using the bent heating body as a heater in the heat-treatment of the reinforcing member. The use of this flexible sheet-like heating body enables the heat-treatment to be applied to the reinforcing members respectively having different diameters. Further, the heater has a relatively simple configuration and is useful. However, this sheet-like heating body, which is formed by bonding a heating element to a surface of an organic resin film, is relatively small in heat capacity per unit area. Thus, in a case where a heat generating portion of the sheet-like heating body has a part, which makes contact with the reinforcing member, and another part that does not make contact with the reinforcing member, the temperature of the part making contact with the reinforcing member is made by a heat transfer action to be constant at a relatively low value. Conversely, the part, which does not make contact with the reinforcing member, causes no heat dissipation due to heat transfer. Therefore, there is a fear that the temperature of this part may excess a heat resistant temperature, and that thus, this part may burn out.